Forums

implementeing IIR (using DSP56k)

Started by cukerek2000 May 14, 2003
Helo,

I'm using DSP563xx and want to implement 2nd order low pass
butterworth IIR filter (fc%0Hz, fsH000). I did something (with do
loop) but it doesn't work correctly. I think that, there is some
problem with coefficients scaling. There is a big difference
betwen "b" and "a" coef.

b =

1.0e-003 *
0.26165269506589 0.52330539013179 0.26165269506589

a = 1.00000000000000 -1.95372794914078 0.95477455992104
Thanks for any help

Jacob




Dear Jacob,

sorry to say, I do not kow what you did exactly (regarding algorithm, filter
form (Direct Form II, II, Canonic or whatever)). I guess that you are trying
to implement a second order biquad filter structure.

To figure out the 'big' difference between "b" (nominator) and "a"
denominator coefficients (which all have to be smaller than 1.0 by the way) I
give you
a link to a Motorola Application Note that unfortunately cannot be found on
their actual
website:

http://www.harmony-central.com/Computer/Programming/fir-iir-filter-app-note.pdf

Please study this carefully in order to stay tuned with the theory which is
the foundation of what you are trying to do right now. This Application Note
helped me a lot when I was in the same situation like you are now some years
before.

Keep on hacking

Christian > Helo,
>
> I'm using DSP563xx and want to implement 2nd order low pass
> butterworth IIR filter (fc%0Hz, fsH000). I did something (with do
> loop) but it doesn't work correctly. I think that, there is some
> problem with coefficients scaling. There is a big difference
> betwen "b" and "a" coef.
>
> b =
>
> 1.0e-003 *
> 0.26165269506589 0.52330539013179 0.26165269506589
>
> a = 1.00000000000000 -1.95372794914078 0.95477455992104 >
> Thanks for any help
>
> Jacob > _____________________________________
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